.NET Framework Standard Library Annotated Reference, Volume 1: Base Class Library and Extended Numerics Library

Example

using System;
using System.Security;
using System.Security.Permissions;
namespace Samples
{
  public class EnvironmentPermissionAccessSample
  {
    public static void Main()
    {
      try
      {
        string ev = "USERNAME";
        EnvironmentPermission p =
               new EnvironmentPermission(
                     EnvironmentPermissionAccess.Read,
                     ev);
        p.PermitOnly();
        Console.WriteLine("Variable {0} is {1}",
                     ev,
                     Environment.GetEnvironmentVariable(ev));
        CodeAccessPermission.RevertPermitOnly();
        p = new EnvironmentPermission(
                     EnvironmentPermissionAccess.NoAccess,
                     ev);
        p.PermitOnly();
        Console.WriteLine("Variable {0} is {1}",
                     ev,
                     Environment.GetEnvironmentVariable(ev));
      }
      catch(SecurityException e)
      {
        Console.WriteLine("Exception: {0}", e);
      }
    }
  }
}

The output is

 Variable USERNAME is damien Exception: System.Security.SecurityException: ...